Simple Generic UITableView Data Source

GenericDataSource.swift

//
//  GenericTableManager.swift
//  Copyright © 2020 andreashanft.de. All rights reserved.
//

import Foundation
import UIKit
import Reusable

/*

 class SomeTableViewCell: UITableViewCell, Reusable {}

 final class SomeTableViewModel {
    @Published private(set) var items = ["Hello World", "Lorem Ipsum", "Don't Picknick"]
 }

 class SomeTableViewController: UIViewController {

     private lazy var dataSource =
         SingleSectionDataSource<String, SomeTableViewCell>(tableView) { (element, cell, indexPath) in
             cell.textLabel?.text = element
         }

     private lazy var tableView = UITableView()
     private var subscriptions = Set<AnyCancellable>()
     private let viewModel: SomeTableViewModel

     private func setupBindings() {
         subscriptions.add([
             viewModel.$items.assign(to: \.items, on: dataSource)
         ])
     }
 }

 */

protocol SectionDefining {
    associatedtype E

    var headerTitle: String? { get }
    var footerTitle: String? { get }
    var elements: [E] { get }
    init(elements: [E])
}

struct GenericSection<E>: SectionDefining {
    var headerTitle: String? { nil }
    var footerTitle: String? { nil }
    var elements = [E]()
}

typealias ReusableTableViewCell = UITableViewCell & Reusable

// MARK: - SingleSectionDataSource

class SingleSectionDataSource<E, C: ReusableTableViewCell>: GenericDataSource<GenericSection<E>, C> {

    public var items: [ElementType] {
        set {
            let section = SectionType(elements: newValue)
            sections = [section]
        }
        get {
            guard let items = sections.first?.elements else {
                return []
            }
            return items
        }
    }
}

// MARK: - GenericDataSource

class GenericDataSource<S, C>: NSObject, UITableViewDataSource, UITableViewDelegate where S: SectionDefining, C: ReusableTableViewCell {

    public typealias CellConfig<Element, Cell> = (Element, Cell, IndexPath) -> Void

    public var sections = [S]() {
        didSet {
            tableView.reloadData()
        }
    }

    typealias ElementType = S.E
    typealias SectionType = S

    private let tableView: UITableView
    private var cellFactory: ((UITableView, IndexPath, ElementType) -> C)

    init(_ tableView: UITableView, cellConfig: @escaping CellConfig<ElementType, C>) {
        self.tableView = tableView
        self.cellFactory = { tableView, indexPath, element in
            let cell: C = tableView.dequeueReusableCell(for: indexPath)
            cellConfig(element, cell, indexPath)
            return cell
        }
        super.init()
        tableView.register(cellType: C.self)
        tableView.dataSource = self
    }

    func numberOfSections(in tableView: UITableView) -> Int {
        sections.count
    }

    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        sections[section].elements.count
    }

    func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        sections[section].headerTitle
    }
    func tableView(_ tableView: UITableView, titleForFooterInSection section: Int) -> String? {
        sections[section].footerTitle
    }

    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let element = sections[indexPath.section].elements[indexPath.row]
        return cellFactory(tableView, indexPath, element)
    }
}